Residents are being urged to be on their guard against telephone fraudsters after a pensioner was tricked out of £10,000.

The man, who is in his 70s and lives in the Steeple Bumpstead area, fell victim to the scam on Tuesday, while a woman of a similar age was also conned out of £5,000 a day earlier in Saffron Walden.

In both cases, the victims were called by a man claiming to be a Metropolitan Police fraud squad officer based at Hammersmith who said he was investigating fraud at their respective banks.

He claimed he needed a large sum to be withdrawn from the local branches of the bank so that the banknotes could be forensically examined.

The money was then collected from their homes but was not returned.

Six other people in north Essex were also contacted on Monday afternoon but fortunately realised it was a scam.

Chief inspector Richard Melton, the Uttlesford and Braintree district commander, said: "These are despicable crimes being carried by thieves posing as police fraud officers, the very people they ought to be able to turn to and trust in exactly this sort of crime.

“Instead, they callously prey on the elderly and vulnerable and have no thought for how their victims might suffer from the loss of money that might have been saved over many years.

"It is vital that whenever people receive this sort of call they should put the phone down and call us, but on another phone or mobile.

“Part of the con involves keeping people on the line while they pretend to transfer calls to police officers or bank officials.”

More than 600 similar thefts and attempted thefts have been reported in Essex since the scam first came to light in January last year, with victims tricked out of more than £325,000.

Six people have already been arrested in connection with the investigation.

To date, most of the thefts or attempted thefts have been in the west and south of the county but rural communities in the Uttlesford and Braintree districts now appear to be being targeted.

Mr Melton said warnings about the scam were also being issued through Neighbourhood Watch groups, community forums and patrolling officers.